The present invention relates to a fuel injector.
German Patent No. 196 42 653 describes a method of metering fuel with a fuel injector. Optimal adjustment parameters for the valve lift of a valve closing body and the injection time are stored in an injection characteristics map for each operating point of the internal combustion engine determined by the rotational speed and the load. In reaching any desired operating point of the internal combustion engine, the corresponding adjustment parameters obtained from the injection characteristics map are used by a control circuit to adjust the valve lift and the injection time for operation of the internal combustion engine. The running smoothness of the internal combustion engine is then measured and compared with an operating point-specific setpoint. If there is a deviation from the setpoint, a regulation unit causes the adjustment parameters to be varied until stabilization of smooth running of the internal combustion engine at the setpoint has been achieved. The adjustment parameters used as the basis for achieving the setpoint are then stored as new optimized values at the operating point in the injection characteristics map, replacing the previous adjustment parameters.
The method described in German Patent No. 196 42 653 for metering fuel with a fuel injector has the disadvantage that the internal combustion engine must first be broken in in order to compile the injection characteristics map. Optimization of the valve lift and injection time depends to a significant extent on the setpoints of the regulation unit, so that under some circumstances an ideal operating point is not achieved. In addition, when running smoothness of the internal combustion engine declines due to aging because of a deviation, which is measured but does not depend on the adjustment parameters, in the running smoothness of the internal combustion engine from a setpoint, deregulation of the adjustment parameters may occur at the operating point of the internal combustion engine. Furthermore, the running smoothness of the internal combustion engine depends on numerous factors such as the composition and temperature of the air supplied and the engine temperature, so that preselecting setpoints to be allocated to the injection characteristics map represents a problem.
Another disadvantage is that for each combination of rotational speed and load, both the valve lift and the injection time must be stored, which requires a high storage capacity in a nonvolatile memory.
German Published Patent Application No. 40 05 455 describes a fuel injector having a piezoelectric actuator and a valve closing body operable by an actuator having a valve lift cooperating with a valve seat face provided on a valve seat carrier to form a sealing seat. To open the sealing seat, a voltage is applied to the actuator, and to close the sealing seat, the voltage is switched off. The fuel injector has a fuel intake connection piece through which fuel is conveyed into the fuel injector. Fuel conveyed into the fuel injector is acted upon by a fuel intake pressure using a fuel pump.
The following disadvantages occur with the fuel injector described in German Published Patent Application No. 40 05 455. To inject a maximum quantity of fuel, which is necessary for full-load operation of the internal combustion engine, a high fuel intake pressure is necessary at the given lift of the valve needle and a given maximum switching time. To reduce the quantity of fuel injected by the fuel injector, the switching time of the fuel injector may be shortened first. Since fuel is also sprayed out of the fuel injector during the opening and closing operation, delivery of fuel is unreproducible in the event of short switching times on the order of magnitude of the opening and closing times of the fuel injector. For extremely small quantities of fuel, which are necessary in idling, for example, it is therefore no longer possible to adjust the quantity of dispensed fuel through the switching time. To be able to dispense a required minimal quantity, the fuel intake pressure must therefore be lowered. This situation is especially problematical in supercharged engines, because extremely low switching times are required due to the short maximum injection time, and nevertheless it may be necessary to reduce the pressure.
Another disadvantage is that the cone vertex angle of the injected fuel jet is determined by the geometry of the seat and cannot be altered during operation of the fuel injector.
The method according to the present invention for metering fuel using a fuel injector has the advantage over the related art that by determining the fuel flow as a function of several settings of the control signal, a fitted curve characterizing the design of the fuel injector is obtained, so that when using the fitted curve, any desired fuel flow may be adjusted using the control signal. By integration of fuel flow over injection time, the quantity of fuel sprayed by the fuel injector may be determined. Thus, at each operating point of the internal combustion engine, a preselected fuel flow may be set by the control signal. It is therefore possible to set a setpoint directly without requiring a special regulation. In addition, it is readily possible to compensate for engine-specific fluctuations.
It is advantageous that by varying the control signal, a cone vertex angle of a fuel jet sprayed by the fuel injector is varied. This makes it possible to preselect the spatial area in which fuel is mixed thoroughly with combustion air.
It is advantageous that the cone vertex angle of the fuel jet sprayed by the fuel injector is measured as a function of the control signal for generating a characteristic curve, and that by using this characteristic curve, a predetermined cone vertex angle of the fuel jet is set with the control signal. This makes it possible to directly adjust a setpoint of the cone vertex angle without requiring any special regulation, and in addition, it is readily possible to compensate for engine-specific fluctuations.
In an advantageous manner, fuel supplied to the fuel injector is acted upon by a fuel intake pressure which is at least approximately constant over time. This simplifies control of the fuel injector.
It is also advantageous if fuel is injected directly into a combustion chamber of an internal combustion engine and if the control signal is influenced by at least one controlled variable of the internal combustion engine. This controlled variable may be, for example, the torque or the rotational speed of the internal combustion engine, or the controlled variable may depend on the composition of the exhaust gas generated by the internal combustion engine. This makes it possible to achieve cylinder balancing and optimization of engine performance. Likewise, long-term drift of the fuel injector may also be compensated. It is especially advantageous if the controlled variable is determined individually for each individual cylinder of the internal combustion engine, so it is possible to rapidly detect a difference in performance of the individual cylinders.